README.md

Groom your app’s Ruby environment with rbenv.

Use rbenv to pick a Ruby version for your application and guarantee
that your development environment matches production. Put rbenv to work
with Bundler for painless Ruby upgrades and
bulletproof deployments.

Powerful in development. Specify your app's Ruby version once,
in a single file. Keep all your teammates on the same page. No
headaches running apps on different versions of Ruby. Just Works™
from the command line and with app servers like Pow.
Override the Ruby version anytime: just set an environment variable.

Rock-solid in production. Your application's executables are its
interface with ops. With rbenv and Bundler
binstubs
you'll never again need to cd in a cron job or Chef recipe to
ensure you've selected the right runtime. The Ruby version
dependency lives in one place—your app—so upgrades and rollbacks are
atomic, even when you switch versions.

One thing well. rbenv is concerned solely with switching Ruby
versions. It's simple and predictable. A rich plugin ecosystem lets
you tailor it to suit your needs. Compile your own Ruby versions, or
use the ruby-build
plugin to automate the process. Specify per-application environment
variables with rbenv-vars.
See more plugins on the
wiki.

How It Works

At a high level, rbenv intercepts Ruby commands using shim
executables injected into your PATH, determines which Ruby version
has been specified by your application, and passes your commands along
to the correct Ruby installation.

Understanding PATH

When you run a command like ruby or rake, your operating system
searches through a list of directories to find an executable file with
that name. This list of directories lives in an environment variable
called PATH, with each directory in the list separated by a colon:

/usr/local/bin:/usr/bin:/bin

Directories in PATH are searched from left to right, so a matching
executable in a directory at the beginning of the list takes
precedence over another one at the end. In this example, the
/usr/local/bin directory will be searched first, then /usr/bin,
then /bin.

Understanding Shims

rbenv works by inserting a directory of shims at the front of your
PATH:

~/.rbenv/shims:/usr/local/bin:/usr/bin:/bin

Through a process called rehashing, rbenv maintains shims in that
directory to match every Ruby command across every installed version
of Ruby—irb, gem, rake, rails, ruby, and so on.

Shims are lightweight executables that simply pass your command along
to rbenv. So with rbenv installed, when you run, say, rake, your
operating system will do the following:

Search your PATH for an executable file named rake

Find the rbenv shim named rake at the beginning of your PATH

Run the shim named rake, which in turn passes the command along to
rbenv

Choosing the Ruby Version

When you execute a shim, rbenv determines which Ruby version to use by
reading it from the following sources, in this order:

The RBENV_VERSION environment variable, if specified. You can use
the rbenv shell command to set this environment
variable in your current shell session.

The first .ruby-version file found by searching the directory of the
script you are executing and each of its parent directories until reaching
the root of your filesystem.

The first .ruby-version file found by searching the current working
directory and each of its parent directories until reaching the root of your
filesystem. You can modify the .ruby-version file in the current working
directory with the rbenv local command.

The global ~/.rbenv/version file. You can modify this file using
the rbenv global command. If the global version
file is not present, rbenv assumes you want to use the "system"
Ruby—i.e. whatever version would be run if rbenv weren't in your
path.

Locating the Ruby Installation

Once rbenv has determined which version of Ruby your application has
specified, it passes the command along to the corresponding Ruby
installation.

Each Ruby version is installed into its own directory under
~/.rbenv/versions. For example, you might have these versions
installed:

~/.rbenv/versions/1.8.7-p371/

~/.rbenv/versions/1.9.3-p327/

~/.rbenv/versions/jruby-1.7.1/

Version names to rbenv are simply the names of the directories in
~/.rbenv/versions.

Installation

Compatibility note: rbenv is incompatible with RVM. Please make
sure to fully uninstall RVM and remove any references to it from
your shell initialization files before installing rbenv.

Homebrew on Mac OS X

As an alternative to installation via GitHub checkout, you can install
rbenv and ruby-build using the Homebrew package
manager on Mac OS X:

$ brew update
$ brew install rbenv ruby-build

Afterwards you'll still need to add eval "$(rbenv init -)" to your
profile as stated in the caveats. You'll only ever have to do this
once.

How rbenv hooks into your shell

Skip this section unless you must know what every line in your shell
profile is doing.

rbenv init is the only command that crosses the line of loading
extra commands into your shell. Coming from RVM, some of you might be
opposed to this idea. Here's what rbenv init actually does:

Sets up your shims path. This is the only requirement for rbenv to
function properly. You can do this by hand by prepending
~/.rbenv/shims to your $PATH.

Installs autocompletion. This is entirely optional but pretty
useful. Sourcing ~/.rbenv/completions/rbenv.bash will set that
up. There is also a ~/.rbenv/completions/rbenv.zsh for Zsh
users.

Rehashes shims. From time to time you'll need to rebuild your
shim files. Doing this automatically makes sure everything is up to
date. You can always run rbenv rehash manually.

Installs the sh dispatcher. This bit is also optional, but allows
rbenv and plugins to change variables in your current shell, making
commands like rbenv shell possible. The sh dispatcher doesn't do
anything crazy like override cd or hack your shell prompt, but if
for some reason you need rbenv to be a real script rather than a
shell function, you can safely skip it.

Run rbenv init - for yourself to see exactly what happens under the
hood.

Installing Ruby Versions

The rbenv install command doesn't ship with rbenv out of the box, but
is provided by the ruby-build project. If you installed it either
as part of GitHub checkout process outlined above or via Homebrew, you
should be able to:

Alternatively to the install command, you can download and compile
Ruby manually as a subdirectory of ~/.rbenv/versions/. An entry in
that directory can also be a symlink to a Ruby version installed
elsewhere on the filesystem. rbenv doesn't care; it will simply treat
any entry in the versions/ directory as a separate Ruby version.

Uninstalling Ruby Versions

As time goes on, Ruby versions you install will accumulate in your
~/.rbenv/versions directory.

To remove old Ruby versions, simply rm -rf the directory of the
version you want to remove. You can find the directory of a particular
Ruby version with the rbenv prefix command, e.g. rbenv prefix
1.8.7-p357.

The ruby-build plugin provides an rbenv uninstall command to
automate the removal process.

Uninstalling rbenv

The simplicity of rbenv makes it easy to temporarily disable it, or
uninstall from the system.

To disable rbenv managing your Ruby versions, simply remove the
rbenv init line from your shell startup configuration. This will
remove rbenv shims directory from PATH, and future invocations like
ruby will execute the system Ruby version, as before rbenv.

rbenv will still be accessible on the command line, but your Ruby
apps won't be affected by version switching.

To completely uninstall rbenv, perform step (1) and then remove
its root directory. This will delete all Ruby versions that were
installed under `rbenv root`/versions/ directory:

rm -rf `rbenv root`

If you've installed rbenv using a package manager, as a final step
perform the rbenv package removal. For instance, for Homebrew:

brew uninstall rbenv

Command Reference

Like git, the rbenv command delegates to subcommands based on its
first argument. The most common subcommands are:

rbenv local

Sets a local application-specific Ruby version by writing the version
name to a .ruby-version file in the current directory. This version
overrides the global version, and can be overridden itself by setting
the RBENV_VERSION environment variable or with the rbenv shell
command.

$ rbenv local 1.9.3-p327

When run without a version number, rbenv local reports the currently
configured local version. You can also unset the local version:

$ rbenv local --unset

Previous versions of rbenv stored local version specifications in a
file named .rbenv-version. For backwards compatibility, rbenv will
read a local version specified in an .rbenv-version file, but a
.ruby-version file in the same directory will take precedence.

rbenv global

Sets the global version of Ruby to be used in all shells by writing
the version name to the ~/.rbenv/version file. This version can be
overridden by an application-specific .ruby-version file, or by
setting the RBENV_VERSION environment variable.

$ rbenv global 1.8.7-p352

The special version name system tells rbenv to use the system Ruby
(detected by searching your $PATH).

When run without a version number, rbenv global reports the
currently configured global version.

rbenv shell

Sets a shell-specific Ruby version by setting the RBENV_VERSION
environment variable in your shell. This version overrides
application-specific versions and the global version.

$ rbenv shell jruby-1.7.1

When run without a version number, rbenv shell reports the current
value of RBENV_VERSION. You can also unset the shell version:

$ rbenv shell --unset

Note that you'll need rbenv's shell integration enabled (step 3 of
the installation instructions) in order to use this command. If you
prefer not to use shell integration, you may simply set the
RBENV_VERSION variable yourself:

$ export RBENV_VERSION=jruby-1.7.1

rbenv versions

Lists all Ruby versions known to rbenv, and shows an asterisk next to
the currently active version.